FDTD Plus
This is a Wiki for a finite-difference time-domain (FDTD) simulation software package developed by the research group of Shanhui Fan at Stanford University. The purpose of this Wiki is to * document the software package. * allow group members to post feedback on the software. = Overview = The name of the FDTD software package is FDTD Plus. Currently, a parallel version of FDTD Plus is available to Fan group members at Shanhuiserve, Bigben, NCSA and SDSC. =User input file= In order to run FDTD Plus, a user input file must be written. This user input file contains details on the structure to be simulated, and the outputs required from the simulation. This section describes the different possible user inputs available. Inputs are grouped into five groups, namely Options, Materials, Sources, Objects and Outputs. = Options = This user input sets up the dimensions, boundaries and cell type for the simulation. syntax: (Option OptionType ) In the definition of the different options below, any option that is not marked "(optional)" is a required option. CellParam Defines the type of cell used in the FDTD computation including the field type. (Option CellParam (CellType value) (FieldType value) (ScalarType value) ) CellType The type of cells used to represent the materials in the computation region, value\in\{linear \} , where linear is a field independent, isotropic (direction-independent) material. FieldType The type of fields within the cell, value\in\{complex, real \} . ScalarType (optional) The scalar type of fields, coefficients etc, value\in\{double, float \} . Default value = double. DimensionParam Defines the spatial and time dimensions of the compute region. (Option DimensionParam (LengthScale (Value value) ) (Center (X value) (Y value) (Z value) ) (Size (X value) (Y value) (Z value) ) (Resolution (X value) (Y value) (Z value) ) (TimeParam (Start value) (End value) ) ) LengthScale (optional) The length scale of the compute region, value\in\mathbb{R}_{>0} . (Note : LengthScale is only required to be defined for frequency dependent or lossy materials). Center The center of the compute region, value\in\mathbb{R} (unit = LengthScale). Size The size of the compute region, value\in\mathbb{R}_{>0} (unit = LengthScale). Resolution The spatial increment in the compute region, value\in\mathbb{R}_{>0} (unit = LengthScale). TimeParam The time parameters for the FDTD run. Start (optional) The start time of computation value\in\mathbb{R} (unit = LengthScale / c, where c = speed of light in vacuum). Default value = 0. End The end time of computation value\in\mathbb{R}_{\geq{Start}} (unit = LengthScale / c). BoundaryParam Defines the boundaries of the compute region. (Option BoundaryParam (Type (X value) (Y value) (Z value) ) (PmlParam (Size (X value1 value2) (Y value1 value2) (Z value1 value2) ) (Type value) (DecayConstant value) ) (BlochKL (X value) (Y value) (Z value) ) (Symmetry (X value) (Y value) (Z value) ) ) Type The type of boundaries in the compute region, value\in\{pml, bloch, none \} , where pml is a Perfectly Matched Layer ([http://en.wikipedia.org/wiki/Perfectly_Matched_Layer PML]) boundary, bloch is a [http://en.wikipedia.org/wiki/Bloch_wave Bloch] boundary, none results in the boundary that includes the origin of the compute region to be of type PEC (E-fields parallel to boundary set to zero), and the opposite boundary of the compute region to be of type PMC (H-fields parallel to boundary set to zero). PmlParam (optional) The parameters for PML boundaries. (Note: PmlParam is only required to be defined if any BoundaryParam::Type pml). Size The size of PML boundaries. (Note 1: Size is included in DimensionParam::Size) (Note 2: Size is only required to be defined for directions with BoundaryParam::Type pml). =value1 = The PML boundary size for boundaries that include the origin of the compute region, value1\in\mathbb{R}_{\geq{0}} (unit = DimensionParam::LengthScale). =value2 (optional = The PML boundary size for boundaries that do not include the origin of the compute region, value2\in\mathbb{R}_{\geq{0}} (unit = DimensionParam::LengthScale). Default value = value2 . Type The type of PML boundary, value\in\{upml \} , where upml is a Uniaxial PML. DecayConstant (optional) The PML decay constant, value\in\mathbb{R}_{>0} (unit = c / DimensionParam::LengthScale). Default value = 1\times{10}^{-6} . BlochKL (optional) The Bloch k-vector for Bloch boundaries, value\in\mathbb{R} (unit = K\:L/2\pi , where K = Bloch k-vector, L = DimensionParam::Size). (Note 1: KL is only required to be defined for directions with BoundaryParam::Type bloch). (Note 2: When BoundaryParam::Type bloch, only KL = 0 allows CellParam::FieldType = real) Symmetry (optional) For a compute region that has mirror symmetry in any direction, this option enforces the symmetry at the center plane normal to that direction (i.e. each symmetry results in a reduction by half of the corresponding DimensionParam::Size used for FDTD computation), value\in\{pec, pmc \} , where pec results in a Perfect Electric Conductor (PEC) center plane where the E-fields parallel to the plane are set to zero. pmc results in a Perfect Magnetic Conductor (PMC) center plane where the H-fields parallel to the plane are set to zero. OutputStructure (optional) Prints the structure within the compute region into a hdf5 file. (Option OutputStructure (FileName value) ) (Note: This option is disabled by default). FileName (optional) The name of the output file, value\in{s}tring . Default value = "structure". (Note: The suffix ".h5" is added to FileName). CheckInput (optional) Option to check the user input file. This option runs the simulation up to the point before cell construction. (Option CheckInput) (Note 1: This option is disabled by default). (Note 2: This option does run OutputStructure if it is enabled). = Materials = This user input defines a material type. syntax: (Material MaterialType (MaterialName value) (MaterialToken value) ) Common material parameters MaterialName The name of the material, value\in{s}tring . (Note 1: Duplicate MaterialName values are not allowed). (Note 2: "vacuum" is a reserved MaterialName). MaterialToken The index of the material (used by OutputStructure to print material), value\in\mathbb{I}_{>0} . (Note 1: Duplicate MaterialToken values are not allowed). (Note 2: 0 is a reserved MaterialToken for "vacuum"). Linear materials These are the material types defined for CellParam::CellType = linear. Lossless Defines a lossless MaterialType. (Material Lossless (MaterialName value) (MaterialToken value) (RelPermittivity value) (RelPermeability value) ) RelPermittivity The relative permittivity of the material, value\in\mathbb{R} . RelPermeability The relative permeability of the material, value\in\mathbb{R} . Lossy Defines a lossy MaterialType. (Material Lossy (MaterialName value) (MaterialToken value) (RelPermittivity value) (RelPermeability value) (Conductivity value) ) The parameters for Lossy is the same as Lossless except for the additional conductivity parameter. (Note: Option::DimensionParam::LengthScale must be defined for Lossy). Conductivity The conductivity of the material, value\in\mathbb{R} . (Unit = siemens/meter). PRP Defines an arbitrary dispersive MaterialType based on general complex-conjugate pole-residue pairs (PRP). (Material Lossless (MaterialName value) (MaterialToken value) (RelPermeability value) (EpsilonInfinity value) (PoleResiduePair (Pair1 pole_value residue_value ) (Pair2 pole_value residue_value ) | | | (PairN pole_value residue_value ) ) ) (Note 1: Option::DimensionParam::LengthScale must be defined for PRP). (Note 2: PRP can be used with Option::CellParam::FieldType = real). EpsilonInfinity The relative permittivity at infinite frequency, value\in\mathbb{R} . PoleResiduePair The N pole-residue pairs, pole\_value,\:residue\_value\:\in\:\mathbb{C} . (Unit = Hertz). (Note: The format for pole_value/residue_value is (real_value, imag_value) ). =Outputs= This user input defines the outputs of the FDTD simulation. syntax: (Output OutputType (StartTime value) (EndTime value) (TimeStep value) (FileName value) ) (Note: The leap frog algorithmn of FDTD results in field components being stored at different time points and different spatial points. Before any output computation below, each field component is spatially averaged (with the corresponding field components in its neighboring cells) to the same spatial point wihin the cell; in addition, time averaging is performed to obtain all field components at the same time point). Common output parameters StartTime The start time of the output, value\in\mathbb{R} (unit = Option::DimensionParam::LengthScale / c). EndTime The end time of the output, value\in\mathbb{R}_{>StartTime} (unit = Option::DimensionParam::LengthScale / c). TimeStep The time step of the output, value\in\mathbb{R} (unit = Option::DimensionParam::LengthScale / c). FileName The name of the file, value\in{s}tring . Outputs FieldTime Output selected fields at a particular point, (Output FieldTime (Position x_value y_value z_value) (OutputField value) (StartTime value) (EndTime value) (TimeStep value) (FileName value) ) Position The position coordinate at which output is performed, x\_value,y\_value,z\_value\in\mathbb{R} . OutputField These are the fields requested. Possible values are dependent on value of CellParam::CellType. (See below for material dependent definitions). FieldSpace Output selected fields in the whole compute region, (Output FieldSpace (OutputField value) (StartTime value) (EndTime value) (TimeStep value) (FileName value) ) (Note 1: The parameters for FieldSpace are similar to FieldTime). (Note 2: The output is performed into a hdf5 file; the suffix ".h5" is added to FileName). (ToDo 1: Only the real part of the field is output currently; need to allow for other outputs). (ToDo 2: To allow the output of the field in a plane instead of the whole region). FluxTimePlane Output the time average Poynting vector S_{avg}=\frac{1}{2}ReE\times{H}^{*} through a plane at each requested TimeStep, (Output FluxTimePlane (Center x_value y_value z_value) (NormalDirection value) (Size value1 value2) (StartTime value) (EndTime value) (TimeStep value) (FileName value) ) (ToDo 1: Implement time average Poynting vector through a box). FluxSpectraPlane Output the transmitted power through a plane as a function of frequency. This involves taking the Discrete Fourier Transform (DFT) of each field parallel to the plane at each point on the plane for the requested length of time, and computing the the complex Poynting vector over the plane at EndTime. The complex Poynting vector is given as S=\frac{1}{2}ReE\times{H}^{*} through a plane, (Output FluxSpectraPlane (Center x_value y_value z_value) (NormalDirection value) (Size value1 value2) (StartTime value) (EndTime value) (TimeStep value) (FileName value) ) (ToDo 1: Implement time average Poynting vector through a box). (ToDo 2: Allow for the imaginary part og complex Poynting vector; this represents the difference in magnetic and electric energy field). Linear material outputs This section defines the material dependent parameters and computation related to outputs for CellParam::CellType = linear. OutputField The fields requested, value\in\{all, ex,ey,ez,hx,hy,hz \} . (Note: OutputField can be any combination of above values; for example, (OutputField ex ey hz) will only output Ex-, Ey- and Hz-fields). FluxTimePlane calculation FluxSpectraPlane calculation =Objects= This user input defines the objects that can be built in the compute region. syntax: (Output ObjectType (Center x_value y_value z_value) (MaterialName/SourceName value) (Array (Axis0 x_value y_value z_value) (Axis1 x_value y_value z_value) (Axis2 x_value y_value z_value) (NoPeriod value0 value1 value2) (Period value0 value1 value2) ) ) (Note: Either a Source or Material can be attached to an object). Common object parameters Center The center coordinate of the object, x\_value,y\_value,z\_value\in\mathbb{R} . (unit = Option::DimensionParam::LengthScale). MaterialName/SourceName The MaterialName (SourceName) of a defined Material (Source), value\in{s}tring . (Note: Defining both MaterialName and SourceName for the same object will throw an initialization error. If you want to define a source and a material at the same point, you have to use separate objects.) Array (optional) Creates an array of the object. (Note: In the description of different object types, this optional parameter will be indicated as .) AxisN (N = 0, 1, 2) The Nth axis along which the object is cloned, x\_value,y\_value,z\_value\in\mathbb{R} . (unit = Option::DimensionParam::LengthScale.) Period The spatial increment of the object center along AxisN, value0,value1,value2\in\mathbb{R} , where valueN is the spatial increment along AxisN. (unit = Option::DimensionParam::LengthScale.) NoPeriod The number of periods along AxisN, value0,value1,value2\in\mathbb{I}_{>0} , where valueN is the number of periods along AxisN. Point Builds a point (i.e. populates one cell), (Object Point (Center x_value y_value z_value) (MaterialName/SourceName value) ) Plane Builds a plane, (Object Plane (Center x_value y_value z_value) (MaterialName/SourceName value) )